This invention relates to reclosable packages and the method for making same, and more particularly to packages of food having a lid sealed to the package base which may be lifted from the base and folded about an edge thereof, and resealable about the lifted portion.
Various processed meats, cheeses and other food products are packaged and marketed in transparent flexible thermoplastic packages which have been evacuated and hermetically sealed to maintain the original freshness and texture. Once the seal of such packages are opened, if the contents are not then completely consumed, the balance of the contents must be refrigerated to prevent it from becoming stale within a short time. Repackaging of the remaining product has been the usual manner of preserving the contents, but the prior art relatively recently has developed packaging having resealing means once the package has been opened. Certain of these package resealing means are relatively complex to use properly and require extensive directions on the packages, while others can be destroyed during the original opening procedure due to the packaging material used.
The prior art describes numerous packaging developments developed toward a solution of certain of the aforesaid problems. For example, Griesbach et al U.S. Pat. No. 4,782,951 and Sanborn U.S. Pat. No. 4,437,293 disclose evacuated hermetically sealed packaging having interlocking closure strips which are used for reclosing the package after the original seal has been broken. In the former development the closure strip is outside of a peelable hermetic seal while in the latter the closure strip is inside of a hard or permanent heat seal. Lingenfelter U.S. Pat. No. 3,181,583, and Branson U.S. Pat. No. 4,787,755 show similar closures for a reclosable pouch or bag which is not initially evacuated. Boeckmann et al U.S. Pat. No. 4,896,775 has a cover sealed to a base and has interlockable closure strips about one edge. A rib fastener is integral with or bonded to the cover or lid, and a receiving groove is on a web having a flange bonded to a rim of the base with a frangible tear line in the web thereby forming a double portion. When a sealed tray is to be opened, the tear line is broken and the cover lifted by pulling on the flange of the web. Alternatively, the two portions of the fastener are manufactured separate and bonded to the cover and base. In Fallowfield U.S. Pat. No. 3,676,159 a package is described having a cover and a base, and includes interlocking ribs and grooves for resealing about the entire periphery. The lid and the base are formed by molding rigid polystyrene, the lid having a contour for nesting within a recess formed in the base. Other prior art located during a preliminary patentability search located a number of patents relating to various methods for making packages with reclosable fasteners and means for extruding interlocking profiles onto a film. Examples of United States Patents located include: U.S. Pat. No. 4,859,259 (Scheiber); U.S. Pat. No. 4,824,497 (Tilman); U.S. Pat. No. 4,906,310 (Broderick et al); U.S. Pat. No. 4,741,789 (Zieke et al); U.S. Pat. No. 4,655,862 (Christoff et al); U.S. Pat. No. 4,618,383 (Herrington); U.S. Pat. No. 4,582,549 (Ferrell); U.S. Pat. No. 4,240,241 (Sanborn); and U.S. Pat. No. 4,673,601 (Lamping et al) which discloses a composite film for resealing packages. Other art using resealable adhesive means include the following U.S. Patents: U.S. Pat. No. 4,786,190 (Van Arden et al); U.S. Pat. No. 3,307,773 (Kratzer et al); U.S. Pat. No. 3,310,225 (Hoblit et al); U.S. Pat. No. 4,415,087 (Clayton et al); U.S. Pat. No. 4,486,814 (Yanase); and U.S. Pat. No. 4,498,588 (Scott). A resealable package having an adhesive is also disclosed in applicant's copending patent application Ser. No. 07/379,913 filed on July 14, 1989, now U.S. Pat. No. 4,956,962.
It can therefore be seen that the prior art has endeavored to develop an inexpensive peelable resealable hermetically sealed package which is inexpensive to manufacture in long production runs and easily used by a consumer. It is highly desirable to have a formed base for receiving the food product, and a transparent flexible lid or cover that may be opened to break the seal, yet be readily reclosed by the consumer after a portion of the contents has been removed. It is one thing to have a reclosable package in the form of a bag or the like which is reclosable along one edge, but when the package has a formed base, difficulties are encountered when a relatively rigid base is used in conjunction with a flexible lid. Thus, in the aforesaid Fallowfield patent the lid and the base were both formed from relatively rigid material. In the aforesaid Boeckmann et al patent a complicated zipper-arrangement was proposed. One of the difficulties encountered in having a flexible film lid used with a zipper-type or rib and groove closure is that if the lid is formed with a portion of the closure member misalignment problems occur during production. For example, if, a rib is to be formed on the lid for insertion into a groove about the closure, the fact that the lid material is flexible and stretches results in a misalignment of the rib relative to the groove as the lid is attached to the base during production. This not only provides a seal that leaks but a failure to provide a closure when used by the consumer. This is especially significant when the rib and groove extend about substantial portions of the respective lid and base of the package as a result of the cumulative effect of the stretching.